Why does the inductor coil need a shielding layer?

Generally, when the inductor coil is wound, copper foil is added between the primary and secondary, and the copper foil must be connected to a fixed point. Because the secondary copper foil is inside, it is generally called inner copper foil; and after the coil is wound In the future, a layer of copper foil is added to the outermost side, and the secondary copper foil is called the outer copper foil.

(1) Add a winding or copper foil shielding layer between the primary and secondary, and draw one end from the shielding layer to the primary ground. The main purpose is to return the common mode interference signal of the primary side to the ground through the shielding layer. In this shielding layer, a part of the common mode signal is transmitted to the secondary through the interlayer capacitance between the primary and secondary, which causes EMI problems at the output end.

(2) Add an internal shielding layer to increase the distance between layers, reduce the capacitance between layers, reduce the primary and secondary coupling, and increase leakage inductance!

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